The present invention relates to a semiconductor wafer ID recognition apparatus for recognizing identification information (ID) formed at an arbitration position on a semiconductor wafer, and a semiconductor wafer ID recognition sorter system for transferring the semiconductor wafer to a predetermined position on the basis of the ID recognized by the ID recognition apparatus.
In general, the surface of a semiconductor wafer has a character or sign as identification information (ID) for identifying the semiconductor wafer. The character or sign is formed from a material having a reflectivity different from that of the surface of the semiconductor wafer or is formed by shaving the surface of the semiconductor wafer.
As disclosed in Japanese Patent Laid-Open No. 7-296147 (reference 1), an ID recognition apparatus for automatically recognizing an ID formed at an arbitrary position on a semiconductor wafer has conventionally been known. The ID recognition apparatus disclosed in reference 1 uses a light-receiving element to receive light reflected by the surface of a semiconductor wafer illuminated by an illumination means, uses a recognition means to process an image obtained by the light-receiving element, and thus recognizes an ID.
An ID recognition sorter for performing sorting operation of transferring a semiconductor wafer to a predetermined position has conventionally been known. This sorter is manually operated because of the existence of a wafer state in which an ID is difficult to read in the process. Recently, demands have arisen for automatic read of a wafer ID and sorting operation which can operate online. Automatic read of a wafer ID can use the ID recognition technique described in the ID recognition apparatus.
A conventional ID recognition apparatus reads the ID of a semiconductor wafer under a plurality of preset read optical conditions, then calculates a score representing a read likelihood ratio for each read optical condition, and adopts an recognition result whose score exceeds a predetermined acceptable score, as the ID of the semiconductor wafer.
If, however, this acceptable score is set too low, many mistakes occur; if the score is set too high, no ID can be determined. The conventional ID recognition apparatus sets the acceptable score around 70 in consideration of this situation. In practice, even this score causes many mistakes. Particularly when the lateral stripe of a pattern or the like overlaps a wafer ID, the ratio of character mistakes increases. If a wafer ID is mistaken, the ID recognition sorter using the ID recognition technique erroneously performs sorting operation.